This invention relates to combustors for gas turbine power plants and more particularly to the pilot combustor and construction thereof.
Typically, the pilot combustor is designed to face the front end of the combustion chamber and to include a plurality of nozzles mounted on the front end so as to inject fuel axially into the combustion zone. Pilot combustors are used in a relatively large engine and are operative during the low thrust power levels. The secondary nozzles are utilized for higher thrust levels but may also be actuated during the lower power regimes. In an annular swirl combustor the fuel manifold is, in certain installations, in proximity to the outer shroud and its diffuser. To feed the fuel nozzles for the pilot combustor the fuel lines are typically routed through the support strut of the diffuser to the combustor front end. In this type of installation, at least three diffusers are needed to permit the proper distribution of combustion, cooling and dilution air while allowing for the required routing of the fuel lines.
We found that this invention permits the routing of fuel lines, achieving the required air distribution while eliminating the need for one of the diffusers and its attendant passageways. This particular routing of the fuel line eliminates the necessity of passing through the strut, reducing the envelope for accommodating the pilot combustor, shortening the overall combustor length and thereby, realizing a reduction of engine weight and size and reducing shaft critical speed problems.
According to this invention the pilot combustor is designed to have radial inflow air and fuel nozzles mounted about an annular pilot combustor. The fuel lines are routed through the outer wall instead of the bulkhead on the front of the combustor. Also, the invention contemplates the judicious orientation of the fuel nozzle with respect to the annular pilot combustion chamber so that the hot gases leaving the swirl cups, which house the fuel nozzles and air swirl vanes, impinges on the opposite inner wall of the annular chamber at an angle that is substantially tangential thereto. This avoids localized heat loads requiring less cooling air with an attendant increase in combustor efficiency.